Heat exchanger

ABSTRACT

A heat exchanger includes a plurality of tubes in which a thermal fluid flows, and a tank located at one longitudinal end portion of each tube and is brazed to the longitudinal end portions of the tubes to communicate with the tubes. The tank and the tube are respectively made of clad material plates in each of which a brazing material is clad on at least one surface of a core material. The brazing material of the tank and the brazing material of the tube respectively include Si content. Furthermore, a rate of the Si content in the brazing material of the tank is lower than that in the brazing material of the tube, and is in a range larger than 0% and equal to or smaller than 6%. Thus, meltage of the tube due to molten brazing material can be reduced during brazing of the tube and the tank.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2009-031276 filed on Feb. 13, 2009, the contents of which are incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger in which tubes are bonded to a tank by brazing.

BACKGROUND OF THE INVENTION

A conventional heat exchanger described in JP 2003-75089A is provided with a plurality of tubes each of which is formed by bonding a pair of heat transfer plates at its periphery portions, and a plurality of outer fins bonded to the outer surfaces of the tubes. The pair of heat transfer plates for the tube is brazed at the bonding portion by using a copper-based brazing material, and the outer fins are brazed to the tubes by using a nickel-based brazing material.

In another conventional heat exchanger, a plurality of tubes and a plurality of fins are stacked in a stack direction, and two longitudinal end portions of each tube are inserted respectively into two tanks, thereby assembling the tubes and the tanks. Furthermore, the tubes and the tanks are brazed after the tubes and the tanks are assembled. In the heat exchanger, in order to braze the tubes and the tanks, the tubes and the tanks are made of a clad material plate in which a brazing material containing Si is clad on a core material (e.g., JP 7-305994A).

In the heat exchanger described in JP 7-305994A, the rate of Si content of the brazing material in the clad material plate of the tube is made smaller than the rate of Si content of the brazing material in the clad material plate of the tank, so that a flow of the brazing material in the clad material plate of the tube can be reduced, thereby reducing diffusion of Si contained in the brazing material to the core material in the clad material plate of the tube. In contrast, the flow of the brazing material at the tanks is made smoothly by increasing the rate of Si content in the brazing material of the tank, so that the tank and the tube can be effectively bonded to each other.

However, in the heat exchanger described in JP 7-305994A, because the flow of the brazing material in the tank is made easy, the brazing material at the side of the tank may easily flow to the outer surface of the tube. Thus, the tube may be melted by the molten brazing material based on temperature states of the tube and tank, and insufficient brazing may be caused. in particularly, if a channel of the brazing material is formed by a step portion on the outer surface of the tube, the molten brazing material at the side of the tank may easily flow into the channel on the outer surface of the tube, and thereby the core material of the tube may be easily melted.

SUMMARY OF THE INVENTION

In view of the foregoing problems, it is an object of the present invention to effectively reduce a melted amount of a core material in a tube due to a molten brazing material, when a plurality of the tubes are brazed to a tank for a heat exchanger.

According to an aspect of the present invention, in a heat exchanger that includes a plurality of tubes in which a thermal fluid flows, and a tank located at one longitudinal end portion of each tube and is brazed to the longitudinal end portions of the tubes to communicate with the tubes, the tank and the tube are respectively made of clad material plates in each of which a brazing material is clad on at least one surface of a core material. In the heat exchanger, the brazing material of the tank and the brazing material of the tube respectively include Si content, and a rate of the Si content in the brazing material of the tank is lower than a rate of the Si content in the brazing material of the tube and is in a range larger than 0% and equal to or smaller than 6%. Because the Si content in the brazing material of the tank is set equal to or lower than 6% and is smaller than the rate of the Si content in the brazing material of the tube, the meltage of the tube in the brazing can be made smaller than the half of the thickness of the core material of the tube before the brazing, thereby effectively reducing the meltage of the tube when the tube and the tank are brazed.

The rate of the Si content in the brazing material of the tank may be in a range larger than 0% and equal to or smaller than 5.5%. More preferably, the rate of the Si content in the brazing material of the tank is in a range between 3% and 4%. In this case, the meltage of the tube can be more effectively reduced when the tube and the tank are brazed, thereby accurately brazing the tube and the tank. In contrast, the rate of the Si content in the brazing material of the tube is in a range between 7.5% and 12%, for example.

In the heat exchanger, the tube may have an outer surface provided with a step portion, and the step portion may extend to a connection portion between the tube and the tank. In this case, the molten brazing material may easily flow into the step portion as a channel. Even in this case, because the rate of the Si content in the brazing materials of the tank and the tube is set as described above, the meltage of the tube due to the molten brazing material can be effectively reduced.

In the above heat exchanger, the tank may be located at two end sides of each tube in a tube longitudinal direction to communicate with the tubes at the two end sides of each tube in the tube longitudinal direction.

According to another aspect of the present invention, in a heat exchanger that includes a plurality of tubes in which a thermal fluid flows, and a tank located at one longitudinal end portion of each tube and is brazed to the longitudinal end portions of the tubes to communicate with the tubes. The tank includes a core plate having a plurality of tube insertion portions into which the longitudinal end portions of the tubes are inserted to be bonded to the core plate and a tank body connected to the core plate to define a space in the tank. Furthermore, the core plate of the tank and the tube are respectively made of clad material plates in each of which a brazing material is clad on at least one surface of a core material. In the heat exchanger, the brazing material of the core plate and the brazing material of the tube respectively include Si content, and a rate of the Si content in the brazing material of the core plate of the tank is lower than a rate of the Si content in the brazing material of the tube and is in a range larger than 0% and equal to or smaller than 6%. Even in this case, because the Si content in the brazing material of the core plate bonded to the tube is set equal to or lower than 6% that is smaller than the rate of the Si content in the brazing material of the tube, the meltage of the tube during the brazing can be made smaller than the half of the thickness of the core material of the core plate, thereby effectively reducing the meltage of the tube when the core plate of the tank and the tube are brazed.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments when taken together with the accompanying drawings. In which:

FIG. 1 is a front view showing a condenser which is an example of a heat exchanger according to a first embodiment of the present invention;

FIG. 2 is a graph showing the relationships between a reaching temperature of a tube and a meltage (melted thickness) of the tube, according to the first embodiment;

FIG. 3 is a graph showing the relationships between a rate of Si content in a brazing material of a core plate of a tank and a residual core thickness in the tube after brazing, according to the first embodiment;

FIG. 4 is a perspective view showing a tube with a cross section substantially perpendicular to a refrigerant flow direction in the tube, according to a second embodiment of the present invention; and

FIG. 5 is a cross sectional view showing a cross section of a tube, perpendicular to a refrigerant flow direction in the tube, according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below based on the accompanying drawings. In the following embodiments, the same or corresponding parts are indicated by the same reference numbers in the drawings, and the detail description thereof is omitted.

First Embodiment

A first embodiment of the present invention will be described with reference to FIGS. 1 to 3. In the first embodiment, a heat exchanger is typically used as a condenser (refrigerant radiator) in which a refrigerant circulating in a refrigerant cycle device is cooled by performing heat exchange with cooling air. For example, the refrigerant cycle device may be used for a vehicle air conditioner for conditioning air to be blown into a vehicle compartment. Here, the refrigerant is an example of a thermal fluid used for the heat exchanger.

FIG. 1 shows the condenser according to the first embodiment. The condenser includes a core portion 1 of an approximately rectangular parallelepiped shape, and tanks 4 located at two sides of the core portion 1, as shown in FIG. 1. The core portion 1 is configured by alternately stacking a plurality of flat tubes 2 and a plurality of outer fins 3 in a top-down direction of FIG. 1.

The outer fin 3 is made of an aluminum alloy, and is formed into a corrugated shape so as to facilitate heat exchange between the refrigerant (thermal fluid) and the cooling air.

The tube 2 has therein a refrigerant passage in which the refrigerant flows. For example, a clad material plate is bent to a predetermined shape, and a brazing is performed by using a brazing material of the clad material plate so as to form the tube 2. In the example of FIG. 1, the flat tubes 2 are arranged, such that a longitudinal direction (i.e., tube longitudinal direction) of each tube 2 corresponds to a horizontal direction, and a major-diameter direction in the cross section of the flat tube 2 corresponds to a flow direction of cooling air.

The two tanks 4 are located at two end portions of the tubes 2 in the tube longitudinal direction, and extend in a direction substantially perpendicular to the tube longitudinal direction. The end portions of the tubes 2 in the tube longitudinal direction are bonded to the tanks 4, so that the passages of the tubes 2 communicate with the inner spaces of the tanks 4, respectively. Each of the tanks 4 includes a core plate 4 a made of an aluminum alloy, and a tank body portion 4 b made of an aluminum alloy. The end portions of the tubes 2 and inserts 5 are inserted respectively into insertion holes of the core plate 4 a, and are bonded to the core plate 4 a by brazing. The tank body portion 4 b and the core plate 4 a are bonded by brazing so as to form a tank space.

The inserts 5 are located at two end sides of the core portion 1 in the stacking direction of the tubes 2 so as to reinforce the core portion 1. The inserts 5 are made of an aluminum alloy, and extend in directions parallel to the tube longitudinal direction. The longitudinal end portions of the inserts 5 are connected to the tanks 2, respectively.

The core plate 4 a is formed from a clad material plate in which a brazing material is clad on a surface of a core material positioned at an outside of the tank (i.e., at a side of the tubes 2 of the core portion 1). The core material of the clad material plate for forming the core plate 4 a is made of an aluminum alley. In contrast, the tube 2 is formed from a clad material plate in which a brazing material is clad on a surface of a core material, corresponding to the tube outside surface. The core material of the clad material plate for forming the tube 2 is made of an aluminum alley. In the first embodiment, in order to form the tube 2, the clad material plate is bent to a flat tube shape, such that the cross section of the tube 2, perpendicular to the tube longitudinal direction, is approximately flat along the tube width direction (i.e., tube major-diameter direction) that is perpendicular to the tube longitudinal direction.

The brazing material of the core plate 4 a and the brazing material of the tube 2 contain Si (silicon), respectively. The rate of Si content contained in the brazing material of the core plate 4 a of the tank 4 is made lower than that in the brazing material of the tube 2. In the first embodiment, the rate of Si content contained in the brazing material of the tube 2 is in a range from 7.5% to 12%.

The inventors of the present application studied in detail regarding a suitable range of the Si content in the brazing material of the core plate 4 a, in the condenser having the above structure according to the first embodiment. In the experiments shown in FIG. 2, the relationship between the reaching temperature of the tube 2 during the brazing and meltage (melted thickness) of the tube 2 after brazing is shown, when the brazing materials of the core plates 4 a are respectively set to have the rate of Si content of 4%, 6%, 7.5% and 10% in a condition where the thickness of the core material of the tube 2 before brazing is 0.2 mm.

As shown in FIG. 2, the meltage of the tube 2 becomes larger as the rate of Si content in the brazing material of the core plate 4 a becomes larger.

According to the experiments by the inventors of the present application, the permissible range of the meltage of the tube 2 is equal to or lower than the half of the thickness (e.g., equal to or smaller than 0.1 mm) of the core material in the tube 2 before brazing. Furthermore, the upper limit of the reaching temperature of the tube 2 during the brazing is different based on the specification of the heat exchanger, but is generally a temperature equal to or lower than 600° C.

As shown in FIG. 2, in a case where the rate of Si content in the brazing material of the core plate 4 a is 6%, the meltage of the tube 2 is lower than 0.07 mm when the temperature of the tube 2 is reached to 600° C. In this case, the meltage of the tube 2 sufficiently satisfies the permissible range. Thus, when the rate of Si content in the brazing material of the core plate 4 a is set in a range larger than 0% and equal to or smaller than 6%, that is lower than the rate of Si content of the tube 2, it can effectively reduce the meltage of the tube 2 due to the molten brazing material flowing from the core plate 4 a when the tube 2 and the core plate 4 a of the tank 4 are brazed.

Then, the core plate 4 a, and the tube 2 in which the core material of the clad material plate has a plate thickness of 0.2 mm, are brazed at three brazing temperatures described later, and the relationship between the rate of Si content in the brazing material of the core plate 4 a and the plate thickness (residual core thickness) of the core material of the tube 2 after brazing is obtained, as shown in FIG. 3.

In the experiments of FIG. 3, the three brazing temperatures are set, such that summation temperature ΣΔt is 106, 193 and 207.5. Here, the summation temperature ΣΔt is the summation of temperature difference Δt between the tube 2 and the core plate 4 a from a start time of the brazing to a time without having a temperature difference between the tube 2 and the core plate 4 a. The brazing temperature generally becomes higher as the summation temperature ΣΔt is larger.

FIG. 3 is the graph showing the relationship between the rate of Si content in the brazing material of the core plate 4 a and the residual core thickness in the tube after the brazing when the summation temperature ΣΔt is 106, 193 and 207.5. As shown in FIG. 3, as the summation temperature ΣΔt becomes larger, that is, as the brazing temperature becomes higher, the residual core thickness of the tube 2 becomes smaller, and the meltage (melted thickness) of the tube 2 becomes larger.

As shown in FIG. 3, in a case where the rate of Si content in the brazing material of the core plate 4 a is equal to or lower than 5.5%, the residual core thickness of the core material in the tube 2 after the brazing is 0.1 mm, and the meltage of the tube 2 during the brazing is 0.1 mm. In this case, the meltage of the tube 2 satisfies the permissible range. Generally, the tube 2 and the core plate 4 a are brazed in a temperature range in which the summation temperature ΣΔt is almost not larger than 207.5. Thus, by setting the rate of Si content in the brazing material of the core plate 4 a in a range larger than 0% and smaller than 5.5%, the meltage of the tube 2 during the brazing can become in the permissible range, almost in the generally used brazing temperature.

In the present embodiment, the rate of Si content contained in the brazing material of the core plate 4 a is made lower than the rate of Si content contained in the brazing material of the tube 2, and is in a range larger than 0% and equal to or smaller than 5.5%. Thus, when the tube 2 and core plate 4 a are brazed, the melted amount of the tube 2 due to the molten brazing material of the core plate 4 a can be reduced in the generally used brazing temperature.

In a case where the summation temperature ΣΔt is smaller than 193, when the rate of Si content in the brazing material of the core plate 4 a is equal to or lower than 6%, the residual core thickness of the core material in the tube 2 after the brazing can be made larger than 0.1 mm. That is, the rate of Si content contained in the brazing material of the core plate 4 a can be made lower than the rate of Si content contained in the brazing material of the tube 2, to be in a range larger than 0% and equal to or smaller than 6%. Even in this case, when the tube 2 and the core plate 4 a are brazed, the melted amount of the tube 2 due to the molten brazing material from the core plate 4 a can be reduced.

As shown in FIG. 3, in a case where the rate of Si content in the brazing material of the core plate 4 a is equal to or lower than 4%, the residual core thickness of the core material in the tube 2 after the brazing is equal to or larger than 0.15 mm, and the meltage of the tube 2 during the brazing becomes equal to or lower than 0.05 mm. In this case, the meltage of the tube 2 is equal to or smaller than the quarter of the plate thickness of the core material in the tube 2. Thus, it can further effectively restrict the tube 2 from being melted due to the molten brazing material of the core plate 4 a of the tank 4.

According to the experiments by the inventors of the present application, when the rate of Si content contained in the brazing material of the core plate 4 a is equal to or larger than 3%, the tube 2 and the core plate 4 a can be accurately brazed. Accordingly, when the rate of Si content in the brazing material of the core plate 4 a is set at a value in a range between 3% and 4% that is smaller than the rate of Si content in the brazing material of the tube 2, the tube 2 and the core plate 4 a can be accurately brazed while it can effectively restrict the core material of the tube 2 from being melted due to the molten brazing material during the brazing between the tube 2 and the core plate 4 a.

Second Embodiment

A second embodiment of the present invention will be described with reference to FIG. 4. In the second embodiment, the shape of a tube 2 is made different from the above-described first embodiment.

FIG. 4 is a perspective view with a cross section perpendicular to a refrigerant flow direction in the tube 2 according to the second embodiment. In the second embodiment, the tube 2 is formed from a clad material plate in which a brazing material is clad on one surface of a core material made of an aluminum alley. For example, when the tube 2 is formed, a single clad material plate having a predetermined thickness is bent at a center portion of the single clad material plate in a plate width direction to have a first plate portion 21 and a second plate portion 22 opposite to each other. The first plate portion 21 has an end portion 23 b, and the second plate portion 22 has an end portion 23 a at a position corresponding to the end portion 23 b in the plate width direction. Two end portions 23 a, 23 b of the opposite first and second plate portions 21, 22 are fastened after the bending, so as to form a fastened portion 23, as shown in FIG. 4.

The end portion 23 b of the first plate portion 21 is plastically deformed and is bent to pinch therein the end portion 23 a of the second plate portion 22, and thereby the end portions 23 a, 23 b are mechanically fixed to each other to form the fastened portion 23. That is, the end portion 23 b of the first plate portion 21 is folded to press-pinch the end portion 23 b of the second plate portion 22, thereby forming the fastened portion 23.

In the tube 2 of the second embodiment, the plate width direction corresponds to the tube major-diameter direction perpendicular to the tube longitudinal direction (i.e., refrigerant flow direction in the tube 2). The two end portions 23 a and 23 b are positioned at one end side of the first and second plate portions 21 and 22 in the tube major-diameter direction, and is overlapped with each other in a tube minor-diameter direction that is substantially perpendicular to the tube major-diameter direction and the tube longitudinal direction. That is, because the two end portions 23 a and 23 b are not placed on the same plan, a step portion 20 is formed at the fastened portion 23 on the outer surface of the tube 2. As shown in FIG. 4, the step portion 20 is formed in an entire length of the tube 2 in the tube longitudinal direction. Thus, a step portion corresponding to the step portion 20 of the tube 2 is also formed in the core plate 4 a so that the tube 2 and the core plate 4 a can be effectively bonded to each other. That is, the step portion 20 is formed in the tube 2 continuously along the tube longitudinal direction to extend to the join portion at which the tube 2 is joined with the core plate 4 a.

The opposite first and second plate portions 21, 22 are formed to have flat base portions 24, and protrusion portions 25 protruding outside from the base portions 24. The flat surfaces of the opposite base portions 24 are made to contact in the tube minor-diameter direction, so that a space is defined between the opposite protrusion portions 25 of the first and second plate portions 21, 22, thereby forming a refrigerant passage 26 by the protrusion portions 25 opposite to each other. As shown in FIG. 4, a plurality of the refrigerant passages 26 are formed respectively by the plural pair of the opposite base portions 24 and the opposite protrusion portions 25, and are arranged in the tube major-diameter direction.

In the present embodiment, the step portion 20 is provided on the outer surface of the tube 2 at the end portion of the tube 2 to extend to the connection portion between the longitudinal end of the tube 2 and the core plate 4 a. Thus, when the tube 2 and the core plate 4 a are brazed, the molten brazing material of the core plate 4 a flows into the step portion 20, and flows in the step portion 20 along the tube longitudinal direction. That is, the step portion 20 forms a brazing material channel in which the molten brazing material flows. Accordingly, during the brazing, the molten brazing material may easily flow to the tube 2 from the core plate 4 a, and the tube 2 may be easily melted due to the molten brazing material.

In the second embodiment, the other parts can be made similar to those of the above-described first embodiment. That is, the rate of Si content in the brazing material of the tube 2 and the core plate 4 a is set similar to that of the above-described first embodiment. According to the present embodiment, even in a case where the tube 2 having the step portion 20 at its outer surface and the core plate 4 a are brazed, because the rate of Si content contained in the brazing material of the core plate 4 a is set as in that of the first embodiment, it can effectively restrict the tube 2 from being melted due to the molten brazing material.

Third Embodiment

Next, a third embodiment of the present invention will be described with reference to FIG. 5. In the third embodiment, the shape of the tube 2 is made different from that of the above-described second embodiment.

FIG. 5 is a cross sectional view showing a section substantially perpendicular to the refrigerant flow direction in the tube 2, according to the third embodiment. As shown in FIG. 5, the tube 2 is provided with a tube portion 6 and an inner fin 7. The tube portion 6 defines the outer shell of the tube 2, and is formed into a flat shape in the section substantially perpendicular to the refrigerant flow direction in the tube 2. The inner fin 7 is provided within the tube portion 6 and has a wave shape so as to increase the heat transfer area of the refrigerant flowing in the tube 2. The tube portion 6 and the inner fin 7 are formed from a single clad plate in which a brazing material is clad on one surface of a core material made of an aluminum alloy.

The tube portion 6 is configured of a first flat plate part 61, a second flat plate part 62, a first arced portion 63, and a second arced portion 64. The first flat plate part 61 and the second flat plate part 62 are opposite to each other in a tube minor-diameter direction, and are substantially parallel to each other. The first arced portion 63 and the second arced portion 64 are opposite to each other in a tube major-diameter direction, and are bent to have respectively an arced shape.

Two end portions of the inner fin 7 in the tube major-diameter direction are bent along the inner peripheral surfaces of the first and second arced portions 63, 64 to tightly contact the inner peripheral surfaces of the first and second arced portions 63, 64 within the tube portion 6. For example, the two end portions of the inner fin 7 are bent respectively concentrically with the first and second arced portions 63, 64. The other portion of the inner fin 7 except the two end portions includes wall portions 71 extending in the refrigerant flow direction and have approximately flat shapes, and tip portion 72 each of which connects adjacent wall portions 71. The tip portion 72 is formed in flat to contact the first or second flat plate part 61, 62.

At the first arced portion 63 of the tube portion 6 on an end side (i.e., left end side in FIG. 5) in the tube major-diameter direction, a first bent portion 66 and a second bent portion 67 in the tube portion 6 are overlapped and then are brazed to each other at the overlapped part. Because the tube portion 6 and the inner fin 7 are formed from the single clad plate, the second bent portion 67 bonded to the first bent portion 66 of the tube portion 6 is also used as the end portion of the inner fin 7. As a result, the end portion of the inner fin 7 tightly contacts the first bent portion 66 at the first arced portion 63 of the tube portion 6. The other end portion of the inner fin 7 in the tube major-diameter direction tightly contacts the second arced portion 64 of the tube portion 6.

Because the first bent portion 66 and the second bent portion 67 are overlapped with each other to tightly contact at the first bent portion 63, a step portion 20 is formed on the outer surface of the tube 2 along the entire longitudinal length of the tube 2. Thus, the step portion 20 is also provided at the connection portion between the tube 2 and the core plate 4 a of the tank 4 (see FIG. 1). That is, a part of the step portion 20 is positioned at the connection portion between the tube 2 and the tank 4.

In the present embodiment, the step portion 20 is provided on the outer surface of the tube 2 at the end portion of the tube 2 to be also positioned at the connection portion between the longitudinal end of the tube 2 and the core plate 4 a. Thus, when the tube 2 and the core plate 4 a are brazed, the molten brazing material of the core plate 4 a easily flows into the step portion 20, and flows in the step portion 20 along the tube longitudinal direction. That is, the step portion 20 forms a brazing material channel in which the molten brazing material flows. Accordingly, during the brazing, the molten brazing material may easily flow to the tube 2 from the core plate 4 a, and the tube 2 may be easily melted due to the molten brazing material of the core plate 4.

However, in the third embodiment, the rate of Si content in the brazing material of the tube 2 and in the core plate 4 a is set similar to that of the above-described first embodiment. Accordingly, even in a case where the tube 2 having the step portion 20 at its outer surface and the core plate 4 a are brazed, because the rate of Si content contained in the brazing material of the core plate 4 a and the tube 2 is set as in that of the first embodiment, it can effectively restrict the tube 2 from being melted due to the molten brazing material.

Other Embodiments

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.

For example, in the above described embodiments, the present invention is typically applied to the condenser as a heat exchanger. However, the present invention can be suitably applied to any heat exchanger such as a radiator, an intercooler, an oil cooler or the like.

Furthermore, the heat exchanger may include one tank 4 that is located at one longitudinal end side of each tube 2 to extend in the tube stacking direction and to communicate with the tubes 2, without being limited to the two tanks 4 positioned at the two longitudinal end sides of each tube 2.

That is, in any structure of a heat exchanger having a plurality of tubes 2 and a tank 4 bonded to the tubes 2 at the longitudinal end of the tubes 2, the other configurations of the heat exchanger can be suitably changed without being limited to the examples of the above described first to third embodiments, when the tube 2 and tank 4 are respectively made of clad material plates in each which a brazing material containing Si is clad on at least one surface of the core material, and when the rate of Si content of the brazing material of the tank 4 is in a range larger than 0% and equal to or smaller than 6% and is smaller than the rate of Si content of the brazing material of the tube 2. Furthermore, the tank 4 can be formed into approximately a single cylinder, without being limited to a tank structure in which the tank 4 is configured of the core plate 4 a and the tank body 4 b.

The rate of Si content of the brazing material of the tank 4 may be in a range larger than 0% and equal to or smaller than 5.5%, while being smaller than the rate of Si content of the brazing material of the tube 2. Alternatively, the rate of Si content of the brazing material of the tank 4 may be in a range between 3% and 4%, while being smaller than the rate of Si content of the brazing material of the tube 2. In contrast, the rate of Si content of the brazing material of the tube 2 may be set preferably in a range between 7.5% and 12%, while being larger than the rate of Si content of the brazing material of the tank 4. As an example, the rate of the Si content in the brazing material of the tube 2 may be in a range between 7.5% and 10%, or may be in a range between 10% and 12%.

In the above-described embodiments, the core plate 4 a is formed from a clad material plate in which the brazing material is clad on one surface of the core material, corresponding to the outside of the tank 4. However, the core plate 4 a may be formed from a clad material plate in which the brazing material is clad on one surface of the core material, corresponding to the inside of the tank 4, or the core plate 4 a may be formed from a clad material plate in which the brazing material is clad on both surfaces of the core material corresponding to the outside and the inside of the tank 4.

In the above-described embodiments, the tube 2 is formed from a clad material plate in which the brazing material is applied to one surface of the core material, corresponding to the outside of the tube 2. However, the tube 2 may be formed from a clad material plate in which the brazing material is clad on one surface of the core material corresponding to the inside of the tube, or the core plate 4 a may be formed from a clad material plate in which the brazing material is clad on both surfaces of the core material corresponding to the outside and the inside of the tube 2.

Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims. 

1. A heat exchanger comprising: a plurality of tubes in which a thermal fluid flows; and a tank located at one longitudinal end portion of each tube, and is brazed to the longitudinal end portions of the tubes to communicate with the tubes, wherein the tank and the tube are respectively made of clad material plates in each of which a brazing material is clad on at least one surface of a core material, the brazing material of the tank and the brazing material of the tube respectively include Si content, and a rate of the Si content in the brazing material of the tank is lower than a rate of the Si content in the brazing material of the tube, and is in a range larger than 0% and equal to or smaller than 6%.
 2. The heat exchanger according to claim 1, wherein the rate of the Si content in the brazing material of the tank is in a range larger than 0% and equal to or smaller than 5.5%.
 3. The heat exchanger according to claim 2, wherein the rate of the Si content in the brazing material of the tank is in a range between 3% and 4%.
 4. The heat exchanger according to claim 1, wherein the rate of the Si content in the brazing material of the tube is in a range between 7.5% and 12%.
 5. The heat exchanger according to claim 1, wherein the tube has an outer surface provided with a step portion, and the step portion extends to a connection portion between the tube and the tank.
 6. The heat exchanger according to claim 5, wherein the step portion extends in the entire length of the tube in a tube longitudinal direction.
 7. The heat exchanger according to claim 1, wherein the longitudinal end portions of the tubes are bonded to the tank by using the brazing materials of the tank and the tube.
 8. The heat exchanger according to claim 1, wherein the tank is located at two end sides of each tube in a tube longitudinal direction to communicate with the tubes at the two end sides of each tube in the tube longitudinal direction.
 9. The heat exchanger according to claim 1, wherein the core material in the clad material plate is made of an aluminum alley.
 10. A heat exchanger comprising: a plurality of tubes in which a thermal fluid flows; and a tank located at one longitudinal end portion of each tube, and is brazed to the longitudinal end portions of the tubes to communicate with the tubes, wherein the tank includes a core plate having a plurality of tube insertion portions into which the longitudinal end portions of the tubes are inserted to be bonded to the core plate, and a tank body connected to the core plate to define a space in the tank, the core plate of the tank and the tube are respectively made of clad material plates in each of which a brazing material is clad on at least one surface of a core material, the brazing material of the core plate and the brazing material of the tube respectively include Si content, and a rate of the Si content in the brazing material of the core plate of the tank is lower than a rate of the Si content in the brazing material of the tube, and is in a range larger than 0% and equal to or smaller than 6%.
 11. The heat exchanger according to claim 10, wherein the rate of the Si content in the brazing material of the core plate of the tank is in a range larger than 0% and equal to or smaller than 5.5%.
 12. The heat exchanger according to claim 11, wherein the rate of the Si content in the brazing material of the core plate of the tank is in a range between 3% and 4%. 